Biohazard Mask Filter

ABSTRACT

An exhalate filter medium for a biohazard mask is made of polytetrafluoroethylene (PTFE) and surrounding layers of a wicking material and an antimicrobial material. The exhalate filter may be contained in a removable and replaceable cartridge snap-fit into the surface of a biohazard mask.

RELATED APPLICATIONS

This application is a continuation-in-part, claiming priority toapplication Ser. No. 10/459,417, filed Jun. 11, 2003, “BIOHAZARD MASKSUITABLE FOR CIVILIANS.” The disclosure of the '417 application isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to filter media for masks which protect againstbiological hazards.

BACKGROUND OF THE INVENTION

Recent developments in antimicrobial respirators have taken the approachof filtering exhaled breath as well as inhaled breath (U.S. Pat. No.6,584,976 B2, issued to Japuntich et al.; '417 application, filed byFreriks et al.; both incorporated herein by reference). By filteringexhalation, the wearer is prevented from exhaling both biologic entitiessuch as bacteria and viruses into the environment where they cancontaminate their surroundings and infect other people. Also, they areprevented from exhaling particles which would disturb or contaminateenvironments that are intended to be particularly clean such aspharmaceutical or nanotechnology production facilities.

Unfortunately, there would be problems to overcome with this approach tofiltering. In particular, the filtering of exhalation would likelyresult in moisture build up in the filter media making the pressure drop(resistance) to exhalation extremely high and making respirationdifficult. This would result in frequent changes of respirators orfilters and exposing wearer's and others to unwanted contamination. Thisis particularly true if the filter media is comprised of typical HEPAfiltering material comprised of non-woven fibers. These media wouldbecome saturated with water vapor from the wearers' exhalation and wouldhave to be changed on a frequent basis.

It is desirable therefore to have an exhalation filter unit forrespirators or masks which could maintain low pressure drop, (i.e., lowexhalation resistance) and superior moisture vapor transmission ratewhile trapping bacteria and viruses in the interior of the filter.

Modern membrane technologies have resulted in HEPA level filtrationcharacteristics with very low resistance, but none has been designedspecifically for the filtering of human exhalation or use in respiratorswhich accomplish this purpose. Developments in membrane technology byGore and others (e.g., U.S. Pat. No. 4,187,390, incorporated herein byreference) have shown that extremely high rates of moisture vaportransmission can be achieved using modern membrane manufacturingtechnologies. However, this moisture vapor transmission (MVT) capabilityhas not been integrated with HEPA (High Efficiency Particulatefiltration) level filtration related to antimicrobial filtration,particularly with regard to the filtering of human exhalation until thepresent invention.

Processes for making porous PTFE membranes having customized and uniformpore size are known (e.g., U.S. Pat. No. 5,910,277 to Ishino et al.,incorporated herein by reference), as are inhalation filter unitsemploying PTFE membranes (e.g., U.S. Pat. No. 6,309,438, to Kanno etal). Missing in the art is the use of PTFE membranes which meet thespecialized requirements for exhalation filters, namely, HEPA levelfiltration of bacterial and viral matter, coupled with pressure drop andhigh MVT.

The filter material itself is not the only feature of a filter unitrequiring special design consideration for exhalation. The physicalstructure of an exhalation filter also requires attention. In abiohazard mask suitable for civilian use (or any other mask requiringfiltering), the filter unit structure should be easily replaceable, withminimum discomfort to the user during replacement but maximum safetyduring quarantine conditions.

SUMMARY OF THE INVENTION

The present invention accommodates the above-mentioned goals through anumber of design features, appearing as recited in various instances andcombinations in the appended claims. Generally the present inventionrelates to a filter wherein the moisture vapor transmission efficiencyhas been improved by using a porous PTFE film with a specific porediameter. The moisture vapor transmission can also be unproved by theuse of coatings or layers that enhance either or both of the wicking andevaporative qualities of the PTFE material, or the anti-biologic andanti-viral properties of the filter (e.g., using biocidal materials).

The present invention also contemplates, in another embodiment, a pairof horseshoe shaped filter cartridges, just below the nose portion ofthe mask. These cartridges rest inset into the surface of the mask, butexternal to the valve assembly (which is integral to the mask). Onehorseshoe-shaped filter cartridge is for inhalation, and one forexhalation. The cartridges are snap-fit (in any manner known in theart), and can be ejected (popped out) by pushing a button, or any othersuitable mechanical actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment (embodiment 1) of the present invention is apolytetrafluoroethylene porous film between two layers of nonwovenpolyolefin spun bond which is impregnated with antimicrobial chemicalson the interior side of the filtering element. The purpose of theantimicrobial additives is to provide a lethal environment for biologicstrapped in the media. Hence, this embodiment involves three layers. Themiddle layer is PTFE. This is sandwiched by layers of spun bond, knownin the art to give rigidity to the PTFE membrane. On the layer intendedto be on the face-side of the mask (for exhalate) or the ambient side ofthe mask (for inhalate), antimicrobial chemical is added in sufficienteffective doses, for example, an agent like REPUTEX which works withinthe spunbond material to control the growth of microbes. In thisembodiment and all of the others herein, the PTFE pore size ispreferable 0.1 to 0.4 microns, and most preferably 0.2 microns, in orderto allow maximum transmission of water vapor, with minimum chance forpassage of bacterial or viral matter.

Another embodiment (embodiment 2) involves the same three layerstructure as embodiment 1, but instead of antimicrobial coatings, thereis added a wicking material to the spun bond on the ambient side of theexhalation filter. Such wicking materials may include the DP-988Synthetic-Fiber Hydrophilic Finishing Agent, manufactured byZhangjiagang Duplus Chemical Co., or similar chemicals manufactured byDaiwa Corporation, Japan. These chemicals have the effect of improvingthe transmissivity of water vapor away from the filter unit.

Another embodiment (embodiment 3) involves combining embodiments 1 and 2into a single exhalation filter, in which one side of the membrane hasspun bond impregnated with a wicking material, and the other side of themembrane has spun bond impregnated with an antimicrobial material.

Another embodiment (embodiment 4) involves a four-or-five layer filtermedium according to the respective teachings of embodiments 1 through 3.In this embodiment, one or more of the spun bond layers sandwiching thePTFE membrane may be inert/uncoated. The various wicking andantimicrobial functions described with respect to embodiments 1 through3 would be accomplished by adding an entirely new layer, as desired. Forexample, there may be a five layer filter medium for an exhalationfilter with the top layer (exposed to the ambient) containing thewicking material, the layer below that spun bond, the layer below that aPTFE membrane, the layer below that another spun bond layer, and finallythe bottom layer (exposed to the wearer's exhalate) containing theantimicrobial material. These additional layers may themselves be a baseof spun bond, or may be any other material suitable for holding theapplicable chemicals while exhibiting low pressure drop to easily passbreath.

All of the foregoing embodiments may be included in a filter cartridgestructure designed for easy replaceability. Preferably, the filtercartridge is in the shape of a horseshoe, and has an internal volume(about 1½ inches thick) containing the appropriate filter medium. Theexterior surface of the cartridge includes a grill. The cartridges siton the surface of the mask, just under the nose portion. One is forinhalation, and is removably seated on the mask. One is for exhalation,and is removably seated on the mask. The seating is preferably asnap-fit, where buttons on the mask will permit pop-out removal of eachrespective filter cartridge. Other mechanical actuators are alsocontemplated, e.g., catch releases, slides, etc.

Pop-out ejection of filter cartridges, coupled with snap-fit insertions,permit quick changes. This can be important during quarantineconditions, both for comfort and for the safety of self and others.

It will be appreciated that those skilled in the art may now make manyuses and modifications of the specific embodiments described withoutdeparting from the inventive concepts. The recitation of the featuresand characteristics of the embodiments shown above is not meant to belimiting, but rather exemplary, with the appended claims and theirequivalents defining the patentee's property rights hereunder.

1-5. (canceled)
 6. An exhalation filter medium having an ambient sideand a face side, the medium comprising: (a) a PTFE layer, (b) a firstnonwoven polyolefin spun bond layer positioned on the PTFE layer on theambient side of the medium and including a wicking material; (c) asecond nonwoven polyolefin spun bond layer positioned on the PTFE layeron the face side of the medium and the layer being impregnated with anantimicrobial material; and (d) a third nonwoven and uncoated polyolefinlayer positioned between the first layer and the PTFE layer orpositioned between the second layer and the PTFE layer.
 7. The filtermedium of claim 6 further comprising a third nonwoven polyolefin layerpositioned between the second layer and the PTFE layer and attached toboth layers.
 8. The filter medium of claim 7 further comprising a fourthnonwoven polyolefin layer positioned between the first layer and thePTFE layer and attached to both layers.
 9. The filter medium of claim 8wherein the fourth layer is inert.
 10. The filter medium of claim 6,wherein the PTFE layer has pore sizes within a range of 0.1-0.4 microns.11. The filter medium of claim 6, wherein the PTFE layer has pore sizesof 0.2 microns.
 12. A biohazard mask including separate inhalation andexhalation filters, the biohazard mask comprising: a plurality ofreceptacles for the holding at least a first filter cartridge containingan inhalation filter and a second filter cartridge containing anexhalation filter; the exhalation filter comprising: (a) a PTFE layer;(b) a first nonwoven polyolefin spun bond layer positioned on the PTFElayer and including a wicking material; (c) a second nonwoven polyolefinspun bond layer positioned on the PTFE layer and being impregnated withan antimicrobial material; and (d) a third nonwoven and uncoatedpolyolefin layer positioned between the first layer and the PTFE layeror positioned between the second layer and the PTFE layer.
 13. Thebiohazard mask of claim 12, wherein the PTFE layer has a pore sizewithin the range of 0.1-0.4 microns.
 14. The biohazard mask of claim 13,wherein the PTFE layer has a pore size of 0.2 microns.